An image recording device as illustrated in FIG. 1 is known in the art using an optical beam, for example, from the Japanese Patent Application Publication No. 55-47392 which corresponds to the U.S. Pat. No. 4,046,471.
In FIG. 1, a photographic drum 1 is rotated in the direction shown by the arrow, its main surface is corona-electrified by a charger 2 and then exposed by an optical beam such as a laser beam 3, and a latent charge image is formed on the surface of the photosensitive drum 1. The laser beam 3 scans a first line on the surface of the photosensitive drum 1 substantially parallel to an axis of the photosensitive drum 1, which is called a main-scanning direction. After scanning a first line, the laser beam 3 scans a second line in the main-scanning direction according to rotation of the photosensitive drum 1. A sub-scanning direction is at substantially right angles to the main-scanning direction, in other words, the rotational direction of the photosensitive drum 1 is the sub-scanning direction.
This latent charge image is developed in the well known manner of positive to negative work by a developer 4 and at least one color toner image is formed on the surface of photosensitive drum 1. A recording material such as paper 5 is pressed continuously onto the surface of the photosensitive drum 1 and the above toner image is transferred to the recording paper 5 by the operation of a transferror 6. The toner image transferred to the recording paper 5 is heat-fixed by a fixer 7 and becomes a printed image on the recording paper 5. As for the photosensitive drum 1, the toner remaining on the photosensitive drum 1 is removed by a cleaner 8 after the toner image is transferred to the recording paper 5. The charge remaining on the photosensitive drum 1 is erased by an eraser lamp 9, and the photosensitive drum 1 is brought to the state where printing is possible again as mentioned above.
A toner image is formed on the recording paper 5 by exposure to the laser beam 3 as mentioned above. The recording density of the image in the sub-scanning direction on this recording paper 5 is determined by the scanning line density in the sub-scanning direction of the laser beam 3 and the rotational speed of the photosensitive drum 1, and in this way, the image dimension in the sub-scanning direction of the screen in determined. In addition, the image dimension in the main-scanning direction is decided by the modulation frequency of an image signal for modulating the laser beam 3 and the main-scanning speed of the laser 3.
Scanning by the laser beam 3 according to the above mentioned prior art is carried out at a constant speed using reflected laser light, modulated at a constant modulation frequency from a laser diode 10, by a polygon mirror 13 rotated at a constant speed through a coupling lens 11 and a diaphragm 12, and by focusing it on the surface of the photosensitive drum 1 with a scanning lens 14. In addition, the rotary moving speed of the photosensitive drum 1 is constant. Therefore, an image signal transmitted to the printer at a constant speed can be recorded only by a predetermined fixed image dimension, and images cannot be recorded on paper with an arbitrary dimension of the arbitrary size in the prior art.
The above prior art does not consider recording an image signal whose original is of arbitrary size and has a problem in that it cannot print the image at an arbitrary size corresponding to the dimension of the paper to obtain an arbitrary image whose dimensions are different from that of the originally predetermined format size.
Furthermore, it is known that the host computer having the original signal source can modify the image signal to an arbitrary size, and can transmit the modified image signal to the laser beam printer. (P: J: Burt: Fast filter transforms for image processing, Comput. Graphics, Image Processing, vol. 16, pp. 20-51 (1981)).
However, this causes the host computer to spend more time to control the printer. It also results that the modified image signal looses information because the recording density in the main-scanning direction of the laser beam and the recording density in the sub-scanning direction of the laser beam are constant.